Download A DC Motor Controller Using The ZILOG Z86E06 MCU Application

APPLICATION NOTE
1
A DC MOTOR CONTROLLER USING
THE ZILOG Z86E06 MCU
THIS DC MOTOR CONTROLLER MORE THAN MEETS THE CHALLENGES OF
SMALLER PACKAGING AND HIGHER RELIABILITY.
INTRODUCTION
Many applications such as printers, ATM machines,
robotics, CD players, and disk drives require DC motor
control. Additionally, the demand for smaller packaging
and higher reliability creates a need for more integrated
motor driver solutions. In the past, a DC motor controller
comprised a microcontroller (MCU) and many discrete
components. Presently, advanced IC technology reduces
the drive electronics to just two chips: an MCU and an
integrated motor driver. This application note will present a
DC motor controller, which uses the Zilog Z86E06 MCU
and the National LMD18200 DC Motor Controller IC, that
is both low cost and features a low parts count.
MOTOR CONTROL BASICS
Several DC motor design topologies exist, but certainly the
most widely used method is the “H-bridge” configuration.
This method uses four Bi-polar Junction Transistor (BJT)
or Metal-Oxide Silicon Field Effect Transistor (MOSFET)
devices configured in an “H” pattern (see Figure 1). In the
center of the “H” is the motor itself. To drive the motor in
the forward direction, current flows through Q1 and Q4. To
turn the motor in the reverse direction, Q1 and Q4 are
turned off, and Q2 and Q3 are energized. External logic is
needed to gate the devices. Motor speed is controlled by
the average current flowing in the legs. This is regulated by
a Pulse-Width Modulation (PWM) drive method, which
relies on the duty cycle of a digital output to control the
drive voltage to the MOSFETs (see Figure 2).
Conventional designs require low-pass filtration to produce
a constant DC voltage. Varying the duty cycle of the output
varies the DC voltage. This DC voltage would then drive
the power MOSFETs. The necessary steering logic is
incorporated inside the LMD18200. The PWM is also
accepted without the need for an external low-pass filter.
Since the voltage drop across the collector and emitter can
reach more than 1V during saturation, high heat
dissipation is encountered using BJT devices. MOSFETs,
with their intrinsically low Rds (drain to source turn-on
resistance), are better suited for motor driver applications.
Typically, power MOSFETs need a gate voltage of least 8V
to turn on, which is a problem when using an MCU whose
outputs swing from 0–5V. Special logic MOSFETs have
been developed that have gate turn-on voltages of 5V.
This works fine for the lower legs of the “H” motor drive, but
AP96DZ80500
what about the upper legs? Unfortunately, the upper legs
need a higher gate voltage, due to the fact that the motor's
winding resistance raises the MOSFETs source reference
above ground potential. A separate DC-DC convertor chip
can be used, but this adds more cost and complexity to the
design. The LMD18200 solves this problem by having a
built-in DC-DC convertor.
V Motor
Q1
Q2
MOSFET
MOSFET
DC Motor
Q3
MOSFET
Q4
MOSFET
Figure 1. H-Pattern Motor Driver Configuration
1
Application Note
A DC Motor Controller Using the Zilog Z86E06 MCU
Zilog
HARDWARE DESCRIPTION
The heart of the motor controller is the Zilog Z86E06, an
18-pin, One-Time Programmable (OTP) MCU, which
contains 1KB of ROM, 128 bytes of RAM, 14 I/O lines, two
timer/counters, and two on-board comparators. A block
diagram of the chip is shown in Figure 2. The Z8® MCU is
Output
Input
VCC
clocked by a 4 MHz ceramic resonator, and the motor is
controlled by the National LMD18200. This is a 3A
H-Bridge driver IC with direction and braking logic, along
with thermal and current sensing of the output drivers. The
functional diagram of the LMD18200 is shown in Figure 3.
GND
Machine
Timing & Inst.
Control
Port 3
1/2 Counter/
Timers [1]
XTAL
WDT, POR
ALU
Interrupt
Control
FLAG
Two Analog
Comparators
Register
Pointer
Serial [2]
Register File
60/124 x
8-Bit
Prg. Memory
512/1K x
8-Bit
Program
Counter
Peripheral
Interface
Port 2
Notes:
[1] Z86E03 has one counter/timer.
[2] Serial Perifpheral Interface for the Z86E06 only.
I/O
(Bit Programmable)
Figure 2. Z86E03/E06 Functional Block Diagram
2
AP96DZ80500
Application Note
A DC Motor Controller Using the Zilog Z86E06 MCU
Zilog
Thermal Flag Output
9
Bootstrap 1
1
Output 1
2
Vs
6
Output 2
10
Bootstrap 2
11
1
Thermal
Sensing
Under-Voltage
Lockout
Charge
Pump
Drive
Overcurrent
Detection
Charge
Pump
Drive
Current
Sensing
Current
8 Sense
Output
Shutdown
Direction 3
Brake 4
Input
Logic
PWM 5
7
Ground
Figure 3. LMD18200 Functional Diagram
Referring to the Z86E03/E06 schematic diagram (see
Figure 4), output port pins P34, P35, and P36 of the
Z86E06 provide direction, brake, and PWM signals,
respectively, to the LMD18200. The current sensing is
done with a resistor to ground from pin 8 of the LMD18200.
The current output from this pin is typically 377 µA/per A.
If the motor is rated at 1A, a resistor value is chosen so that
the voltage developed across the resistor does not exceed
4V, which is the maximum input voltage to the comparator
on-board the Z86E06. This calculates out to be 10.6K
ohms (4V/377µA). For this application, the motor was
rated at 12V @ 0.6A. A resistor value of 2.7K ohms was
chosen to give a maximum voltage across the resistor of
approximately 2.5V at all speeds. This voltage is sensed
by one of the Z8® MCU’s on-board comparators. The
reference pin for the comparators (P33) is biased at 3.3V
through a voltage divider.
The temperature flag pin (9) of the LMD18200 is
connected to P32 of the Z8 MCU. This is an open-collector
output, therefore it is pulled up to +5V with a 10K ohm
resistor. The function of this pin is to interrupt the
processor when the junction temperature of the
LMD18200 exceeds 145 degrees C. This is an active-low
output, which will trip the Z8 MCU comparator at P32. A
push button connected to P20-P22 of the Z8 MCU
provides the speed and brake control.
Any significant load on the motor will increase the motor
current, thereby increasing the voltage across the current
sense resistor. If the voltage across the sense resistor
exceeds 3.3V, a comparator interrupt will be generated,
and the BRAKE line to the LMD18200 will be activated,
stopping the motor. When the load condition of the motor
is removed, pressing the STOP push button reactivates
the motor.
The motor terminals are connected between the OUT1
and OUT2 terminals of the LMD18200. The 0.1 µF ceramic
capacitors are connected between the bootstrap pins
(1,11) and motor output pins (2,10). The Vs pin is
connected to +12V. This line is bypassed with a 220 µF
and 0.1 µF capacitors.
AP96DZ80500
The SPDT toggle switch connected to P23 provides the
direction (high is forward, low is reverse). Direction
changing can only be done in a STOP condition. Status
LEDs show the direction and stop conditions. The STOP
LED (red) is connected to P24. The FORWARD (yellow),
and REVERSE (green) LEDs are connected to P25 and
P26, respectively.
3
Application Note
A DC Motor Controller Using the Zilog Z86E06 MCU
Zilog
Figure 4. DC Motor Controller Schematic
4
AP96DZ80500
Application Note
A DC Motor Controller Using the Zilog Z86E06 MCU
Zilog
SOFTWARE DESCRIPTION
The motor controller software flowchart is shown in Figure
5. After initialization, the controller waits for a timer T0
interrupt. The timer interval is set for about 500 µs. This
was chosen to provide a 2000 Hz. sample rate for the
PWM.
The SAMPLE interrupt service routine essentially handles
two functions:
■
The PWM Output
■
Sensing and Debouncing of the Push Button
The comparator interrupts sense overload and overtemperature conditions. (Refer to Code Listing at the
conclusion of this application note.)
Initialization
1. Set PWM for 50%.
2. Set brake bit.
3. Turn on Stop LED.
4. Load and enable timers.
5. Enable interrupts.
A
Decrease
Button?
Wait for Interrupts
Yes
Debounce
Count
Reached?
Save
Button
Status
Yes
No
Brake
Button?
No
No
PWM
at MIN?
Yes
T0 Interrupt
Yes
1. Set P36 High
2. Reload and enable controls
Any
Buttons
Down?
No
1. Toggle brake bit
2. Toggle stop LED
1. DEC PWM
2. Load T1 with
PMW count
Exit
B
Exit
Yes
Increase
Button?
No
Yes
Debounce
Count
Reached?
No
Save
Button
Status
Over-temperature interrupt routine
Set brake bit
Yes
A
Yes
Return
PWM = MAX?
Over-current interrupt routine
1. Increment PWM
2. Load T1
Set brake bit
Return
B
Figure 5. DC Motor Flowchart
AP96DZ80500
5
1
Application Note
A DC Motor Controller Using the Zilog Z86E06 MCU
Zilog
Refer to Figure 6 for PWM Waveforms. The initial PWM is
set for a 50-percent duty cycle. The initial state is STOP,
as indicated by the red LED. The motor may be taken out
of STOP by momentarily pressing the STOP button. The
motor will then turn at a speed determined by the PWM
value and either clockwise or counterclockwise, as
determined by the DIRECTION switch. The duty cycle of
the PWM is controlled by timer T1. This is loaded with a
value contained in register PWM. The timer is configured
to count down, then stop when it reaches zero. When it hits
terminal count, it toggles port pin P36 from high to low. The
timer is loaded with its initial value, and P36 is taken high
on the next pass of the T0 interrupt interval. The timer T0
sets the sampling rate, in this case 2000 Hz.
Pressing the INCREASE push button increases the duty
cycle of the PWM, while the DECREASE push button
decreases the duty cycle of the PWM. The maximum limits
are 240/256 (93 percent) and 32/256 (12.5 percent),
respectively. Pressing the STOP button toggles the
BRAKE output to the LMD18200, and either brakes or
enables the motor, depending on the present state.
A
B
C
A = 33%
B = 50%
C = 84%
Figure 6. PWM Waveforms Duty Cycle
The temperature flag input to the Z8® MCU senses the
condition of this signal from the LMD18200. This pin goes
active low when the junction temperature of the motor
controller reaches 145 degrees C. The assertion of this pin
(active low) causes the compartor to trip at P32,
interrupting the processor. The OVER_TEMP interrupt
service routine sets the BRAKE output to high, disabling
the motor. This condition will exist until the THERMAL
FLAG bit goes high again.
REMOTE CONTROL
Instead of push button switches to control the functions
and speed of the motor, an I2C or asynchronous communications protocol can be added for remote control.
REFERENCES
Speed
4. Zilog, Zilog Discrete Z8 Microcontrollers Product
Specifications Databook, DC 8318-02.
2. Jeff Bachiacchi, “Creating The Smart-MD,” Circuit
Cellar Ink, September–October,1995.
5. Zilog, Zilog Z8 Microcontroller User’s Manual,
UM95Z800103.
3. National Semiconductor, LMD18200 datasheet.
˙
1. Chuck McManis, “A PIC-based Motor
Controller,” Circuit Cellar Ink , July, 1995.
6
AP96DZ80500
Application Note
A DC Motor Controller Using the Zilog Z86E06 MCU
Zilog
CODE LISTING
asmS8 version 2.1
Tue Feb 27 02:59:25 1996
LOC
OBJ
abs
abs
abs
abs
abs
abs
abs
abs
abs
abs
abs
abs
00000004
00000005
00000006
00000007
00000008
00000009
0000000a
0000000b
0000000c
0000000e
0000000f
0000000e
00000000000000000001
00000000000000000002
00000000000000000003
00000000000000000008
00000000000000000007
00000000000000000020
000000000000000000e0
00000000000000000001
00000000000000000004
00000000000000000010
00000000000000000020
00000000000000000040
AP96DZ80500
1
b:\testdnm
LINE# --- SOURCE --1 ;---------------------------------------------------------------------------2 ;
This program is intended to control a DC motor with a Zilog
3 ;
microcontroller. The Z8 produces a PWM (Pulse-Width Modulation) signal
4 ;
that drives a National LMD18200 H-bridge motor driver. This allows
5 ;
full directional and speed control of the motor. The speed,
6 ;
direction, and stop functions are controlled by pushbutton switches.
7 ;
A status LED indicates Forward (Green), Reverse (Yellow), and Stop
8 ;
(Red) conditions. A voltage feedback from the H-bridge allows the
9 ;
microcontroller to monitor the current through the motor. This is
10 ;
implemented with a series resistor from the Is pin of the H-bridge,
11 ;
and the voltage developed across the resistor is proportional to the
12 ;
current through the motor. This voltage is fed back to one of the Z8's
13 ;
on-chip analog comparators.
14 ;
15 ;
16 ;
17 ;
Z86E06 pin assignments
18 ;
--------------------19 ;
1
18
20 ;
--------------21 ;FORWARD LED - | P24
P23 | - DIR SWITCH
22 ;
|
|
23 ;REVERSE LED - | P25
P22 | - STOP PUSHBUTTON
24 ;
|
|
25 ;
STOP LED - | P26
P21 | - SPEED DECREASE PUSHBUTTON
26 ;
|
|
27 ;
N/C - | P27
P20 | - SPEED INCREASE PUSHBUTTON
28 ;
|
|
29 ;
+5V
| Vcc
GND | - GND
30 ;
|
|
31 ;
OSC
| Xtal1
P36 | - PWM OUT
32 ;
|
|
33 ;
OSC
| Xtal2
P35 | - STOP
34 ;
|
|
35 ;
Vref | P33
P34 | - DIRECTION
36 ;
|
|
37 ;
Tf
| P32
P31 | - Is
38 ;
--------------39 ;
9
10
40 ;
41 ;---------------------------------------------------------------------------42
43 bounce
.equ
r4
44 count
.equ
r5
45 key_cnt
.equ
r6
46 key_temp
.equ
r7
47 temp_1
.equ
r8
48 pwm
.equ
r9
49 make
.equ
r10
50 STATE
.EQU
R11
51 temp_led
.equ
r12
52 delay_hi
.equ
r14
53 delay_lo
.equ
r15
54 delay
.equ
rr14
55
56 increase
.equ
01h
57 decrease
.equ
02h
58 brake
.equ
03h
59 dir_sw
.equ
08h
60 switches
.equ
07h
61 min
.equ
20h
62 max
.equ
0e0h
63 irq0
.equ
01h
64 irq2
.equ
04h
65 irq4
.equ
10h
66 brakes_on
.equ
20h
67 stop_led
.equ
40h
7
Application Note
A DC Motor Controller Using the Zilog Z86E06 MCU
00000000000000000020
00000000000000000010
00000000000000000000
00000000000000000001
00000000000000000002
00000000
00000000
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00000006
00000008
0000000a
Wwww
Wwww
Wwww
Wwww
Wwww
Wwww
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a6eb00
eb**
760208
6b**
460310
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Zilog
reverse_led
.equ
20h
forward_led
.equ
10h
stopped
.equ
00h
start_up
.equ
01h
running
.equ
02h
;---------------------------------------------------------------------------;
INITIALIZATION
;---------------------------------------------------------------------------.org
0000h
.word
.word
.word
.word
.word
.word
over_temp
no_irq
over_current
no_irq
sample
no_irq
.org
000ch
di
; disable int
srp
#0
; lowest bank
ld
p2m,#0fh
; inputs on p20-p23, outputs on p24-p27
ld
p2,^C #stop_led
; load with initial values
ld
p3m,#2
; open drain on P2, comparators on
ld
p01m,#04h
; int stack
ld
spl,#80h
; stack at highest ram location
clr
sph
; clear stack pointer high byte
clr
irq
; clear int request reg
ld
pre0,#04h
; load prescaler 0 with /1, one-shot
clr
t0
; set timer TC for period of 0.5 mS
ld
imr,#irq4
; set interrupt levels
ld
pre1,#06h
; one shot
ld
p3,#60h
; brakes on, pwm high
ld
STATE,#stopped
;
clr
ipr
;
clr
delay_hi
;
clr
delay_lo
;
ld
pwm,#80h
; start with pwm = 50%
ld
t1,pwm
; load timer with pwm value
ld
tmr,#8fh
; load and enable t0,t1
ld
irq,#80h
; rising on irq2, falling on irq0
delay_loop:
ei
; enable interrupts
jr
delay_loop
; wait for interrupts
;---------------------------------------------------------------------------;
OVER-TEMPERATURE INTERRUPT ROUTINE
;---------------------------------------------------------------------------over_temp:
or
p3,#brakes_on
; set BRAKE line high
ld
STATE,#stopped
;
ld
p2,^C #stop_led
;
ld
imr,#irq4
;
iret
; return from interrupt
;---------------------------------------------------------------------------;
OVER-CURRENT INTERRUPT ROUTINE
;---------------------------------------------------------------------------over_current:
or
p3,#brakes_on
; set BRAKE line high
ld
STATE,#stopped
;
ld
p2,^C #stop_led
;
ld
imr,#irq4
;
iret
;
;---------------------------------------------------------------------------;
TIMER 0 INTERRUPT ROUTINE
;
;
This routine performs the following functions:
;
;
1) Sets sample rate for PWM at 2000 Hz
;
2) Tests for key closures and checks direction switch
;---------------------------------------------------------------------------sample:
cp
STATE,#stopped
; check if stopped
jr
ne,test_start_up;
tm
p2,#dir_sw
; test direction switch
jr
z,ccw
; if low, then reverse
or
p3,#10h
; if high, then forward
AP96DZ80500
Application Note
A DC Motor Controller Using the Zilog Z86E06 MCU
Zilog
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ccef
8b**
5603ef
ccdf
a6eb01
eb**
80ee
eb**
e6fb15
bc02
460340
e6f18f
660207
6b**
8802
5c03
6e
df
c0e8
7b**
a276
eb**
4e
a6e480
7b**
a6e601
eb**
a6e9e0
6b**
9e
99f2
8b**
a6e602
eb**
a6e920
3b**
00e9
99f2
8b**
a6e603
eb**
a6eaff
6b**
b60320
acff
760320
eb**
c902
bc01
8b**
bc00
e6fb10
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8b**
78e6
b0e6
bf
5aa4
b0ea
b0e4
b0e6
b0e7
b0e5
bf
AP96DZ80500
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ccw:
test_start_up:
continue:
key_scan:
key_loop:
try_decrease:
try_brake:
test_dir:
load_keys:
no_keys:
exit:
exit_1:
no_irq:
ld
jr
and
ld
cp
jr
decw
jr
ld
ld
or
ld
tcm
jr
ld
ld
inc
scf
rrc
jr
cp
jr
inc
cp
jr
cp
jr
cp
jr
inc
ld
jr
cp
jr
cp
jr
dec
ld
jr
cp
jr
cp
jr
xor
ld
tm
jr
ld
ld
jr
ld
ld
ld
ld
jr
ld
clr
iret
djnz
clr
clr
clr
clr
clr
iret
temp_led,^C #forward_led
continue
;
p3,^C #10h
;
temp_led,^C #reverse_led
STATE,#start_up
;
ne,continue
;
delay
;
nz,continue
;
imr,#irq4+irq2+irq0;
STATE,#running
;
p3,#40h
;
tmr,#8fh
;
p2,#switches
;
z,exit
;
temp_1,p2
;
count,#3
;
key_cnt
;
;
temp_1
;
c,no_keys
;
key_temp,key_cnt
;
ne,load_keys
;
bounce
;
bounce,#80h
;
ult,load_keys
;
key_cnt,#increase
;
ne,try_decrease
;
pwm,#max
;
eq,exit
;
pwm
;
t1,pwm
;
exit
;
key_cnt,#decrease
;
ne,try_brake
;
pwm,#min
;
ule,exit
;
pwm
;
t1,pwm
;
exit
;
key_cnt,#brake
;
ne,exit
;
make,#0ffh
;
eq,exit_1
;
p3,#20h
;
make,#0ffh
;
p3,#20h
;
nz,test_dir
;
p2,temp_led
;
STATE,#start_up
;
exit_1
;
STATE,#stopped
;
imr,#irq4
;
temp_led,p2
;
p2,^C #stop_led
;
exit_1
;
key_temp,key_cnt
;
key_cnt
;
;
count,key_loop
;
make
;
bounce
;
key_cnt
;
key_temp
;
count
;
;
take direction bit low
1
take pwm high
load and enable timer
any switches pressed?
no, then exit
get switch data
load counter
inc key count
set carry flag
rotate right
any carry?
same key?
not the same
increment bounce counter
bounce = 127 ?
no action if less
increase key?
no, try decrease key
are we at maximum pwm?
yes, don't increment
increment pwm (increase speed)
load timer with pwm value
exit routine
decrease key?
try brake key
is pwm at minimum?
if yes, don't decrement
decrement pwm (decrease speed)
load new pwm value
exit
brake button down?
exit if not
button still down?
yes - take no action
toggle brake bit
set make flag
brake high?
test dir sw if brakes are on only
load direction led
motor turning
exit
get led data
turn on stop led
transfer key data
clear key register
return to interrupt
tested all keys?
clear key registers
return from interrupt
.end
9
Application Note
A DC Motor Controller Using the Zilog Z86E06 MCU
© 1997 by Zilog, Inc. All rights reserved. No part of this document
may be copied or reproduced in any form or by any means
without the prior written consent of Zilog, Inc. The information in
this document is subject to change without notice. Devices sold
by Zilog, Inc. are covered by warranty and patent indemnification
provisions appearing in Zilog, Inc. Terms and Conditions of Sale
only. Zilog, Inc. makes no warranty, express, statutory, implied or
by description, regarding the information set forth herein or
regarding the freedom of the described devices from intellectual
property infringement. Zilog, Inc. makes no warranty of
merchantability or fitness for any purpose. Zilog, Inc. shall not be
responsible for any errors that may appear in this document.
Zilog, Inc. makes no commitment to update or keep current the
information contained in this document.
10
Zilog
Zilog's products are not authorized for use as critical components
in life support devices or systems unless a specific written
agreement pertaining to such intended use is executed between
the customer and Zilog prior to use. Life support devices or
systems are those which are intended for surgical implantation
into the body, or which sustains life whose failure to perform,
when properly used in accordance with instructions for use
provided in the labeling, can be reasonably expected to result in
significant injury to the user.
Zilog, Inc., 210 East Hacienda Ave.
Campbell, CA 95008-6600
Telephone (408) 370-8000
FAX (408) 370-8056
BBS (408) 370-8024
Internet: http://www.zilog.com
AP96DZ80500